1. Field of the Invention
The present invention relates to a digital-to-analog converting device.
2. Description of the Prior Art
For example, a digital audio apparatus is known in which a sampled acoustic signal is converted to a one-bit serial data pulse train by means of the PDM (Pulse Density Modulation) technique, i.e. using e.g. a noise shaper, and the data pulses are reproduced as an acoustic signal by adding them together in an analog manner.
In the above circuit arrangement, sampling data of about 44 KHz is converted to a data pulse train of a very high frequency, i.e. about 11 MHz, so that the rising and falling portions of one such data pulse can amount to a significant proportion of the overall pulse. For this reason, when the rise and fall times differ from each other as shown at A in FIG. 5, a multiple pulse consisting of a plurality of coupled pulses will contain a data pulse P1 at the rising portion whose area is further significantly different from that of the other data pulses P2.
Further, if the data pulses have a long fall time, a data pulse P3 can accidentally overlap with another data pulse P4, as shown in FIG. 5B. Thus, such data pulses, when converted into an analog output, will produce an error which causes the digital-to-analog conversion characteristics to become nonlinear, deteriorating the tone quality.
An object of the present invention is therefore to improve the digital-to-analog conversion characteristics by means of an arrangement in which data pulses are all converted into pulses having an identical waveform and an identical area.